1. Field of the Invention
This invention relates generally to a method and apparatus for digital printing and, more specifically, to a method and apparatus that employs a metering device for metering a quantity of paint to be deposited on a surface to be painted and that deposits the metered quantity of paint on the surface.
2. Background of the Invention
Large format printing, such as the printing of billboard signs and building drapes, has generally followed printer technologies used in smaller scale printers, such as thermal and piezoelectric ink jet technologies. Such technologies, when employed for large scale printing, are relatively expensive, with large format thermal ink jet printers costing the range of about $250,000 to $350,000 and large format piezoelectric printers costing about $700,000 to $800,000.
Such ink jet printers work by depositing small droplets of ink in various colors, typically cyan, magenta, yellow and black, on a print medium to form a color image. Conventional thermal ink jet printing heads include a plurality of nozzles and thermal elements. Ink is expelled from the nozzles in a jet by bubble pressure created by heating the ink by the thermal elements while the nozzles and thermal elements are in close proximity. One such ink jet printing head, as described in U.S. Pat. No. 5,121,143 to Hayamizu, includes a thermal head member having at least one thermal element consisting of a plurality of thermal dot elements and a plurality of electrodes of different widths connected to each thermal element whereby different widths of heated portions of the thermal element are obtainable to vary the amount of ink jetted in one dot. Another such ink jet printing head is described in U.S. Pat. No. 4,731,621 to Hayamizu et al.
Another type of print head is disclosed in U.S. Pat. No. 4,764,780 to Yamamori et al. in which an ink ejection recording apparatus includes a plurality of ink ejection heads connected to an ink tank, each of the ink ejection heads having an ink nozzle through which minute ink droplets are discharged in accordance with an electric signal and an air nozzle opposing the ink nozzle and adapted for forming an air stream which accelerates the ink droplets toward a recording medium.
Typical desk top ink jet printers for home or office use are relatively inexpensive but are usually limited to printing on standard office size sheets of paper, such as 8xc2xdxc3x9711 or similar standard sizes. Some wide format printers, however, are able to accommodate 16 feet or wider substrates such as films, paper, vinyl, and the like and can print 300 ft2 per hour, depending on the resolution of the print. Such machines sometimes employ piezoelectric printhead technology utilizing several printheads per color with numerous nozzles per printhead to deposit ink onto the print medium.
In addition to the cost of the machine itself, which employs relatively small orifices, valves and nozzles for depositing the desired quantity and color of ink on the print medium, very fine grade inks are required in which particle sizes of the pigments within the inks are kept to a minimum to help keep the orifices, valves, and nozzles of the ink system from becoming clogged. Such inks are expensive and thus result in billboard sized prints to be rather expensive. Despite the high quality and expense of ink products, clogging of the printhead is still a problem with current printer technologies.
Many large format printers also use water-based inks that may not be suitable for outdoor use. Accordingly, special waterproofing systems and techniques must be employed such as treating the printing medium with a substance that binds with the ink once deposited to form a waterproof mark or laminating the print with a weatherproof film. These weatherproofing techniques and processes add expense to the cost of each print.
There are some applications for digital printing where the resolution is not a significant issue. These applications include very large signage such as large billboard signs or building drapes as were used in the 2002 Salt Lake City Winter Olympics. Billboards, which are typically about 14 feetxc3x9748 feet do not require extremely sharp resolution as the viewing distances are typically more than 100 feet away. Another application in which lower resolution imaging may have significant usefulness is in stadium graphics such as printing on football field end zones (both grass and artificial turf), grass infields of race car tracks and foul territories and warning tracks of baseball fields. Military applications include applying camouflage painting schemes to ship hulls, decks and structures, as well as tanks and large decoys. Other applications may include the printing of imagery on freeway embankments, roadways, and roof tops. Still other applications may include printing on carpet and other textiles. To obtain sufficient image coverage, large quantities of pigmented paint or sublimating dye are very desirable to produce a highly visible image. In situations where the media is a building drape, a rocky embankment, plush carpeting, or a grass field, such large quantities of paint are necessary to fill voids in media so that the desired image is visible. The volumes of paint needed to produce such images are much greater than ink jet technology could ever reasonably deliver. As such, current methods of painting football end zones include hand painting with rollers and other conventional paint application devices to produce a desired image. Such methods are extremely time consuming and require significant manpower to accomplish.
In the case of building drapes, such as those used in the 2002 Winter Olympics in Salt Lake City, the fabric was a screen-type material that would allow air to easily pass through the fabric. Because of the difficulty in applying paint to such materials using current state of the art techniques, the building drapes were not only of quite low resolution, but were generally washed out in both vibrancy and color.
Thus, it would be advantageous to provide a method and apparatus for producing images on virtually any medium including highly porous media or media having significant voids where large quantities of paint are necessary to produce a desired image. Furthermore, it would be highly advantageous to provide a method and apparatus for digital printing that is compatible with any paint including fast drying paints such as all surface acrylic enamels. It would be a further advantage to provide a method and apparatus for digital printing that is compatible with extremely inexpensive paints, such as common house paints. Digital printing with sign type ink jet inks can run up to $0.50 per square foot. Typical ink prices run $0.20 per square foot. Cheap house paint can result in digital imaging paints costing between 2 and 3 cents per square foot. Such capability is very significant in large signage applications which are now near commodity based pricing.
Accordingly, a paint injector is provided comprising at least one air nozzle that directs a jet of air across a moving member, the member having ink, paint, or other similarly pigmented liquid material disposed thereon. The air jet blows or pulls the paint off of the member and onto a print medium, such as paper, vinyl, film, grass, dirt, rock, asphalt, carpet, fabric or other textiles, or other print media known in the art. The moving member is comprised of a wheel having paint disposed on the outer rim or edge thereof.
In one embodiment, a relatively small saw-type blade or gear may be used as a miniature gear pump to meter paint for digital printing. The edge or teeth of the gear or blade grab paint within the gap between each tooth from a paint reservoir. The blade is advanced between a pair of air jets and the paint in the gap is blown off from both sides of the blade. As the blade continues to rotate it interlocks with a second blade having substantially the same teeth spacing and configuration. The engagement of the teeth between the first and second blades causes any paint remaining between each tooth of the first blade to be forced out by the interlocking nature of the blades. As the paint is removed from the teeth of the first blade, small scrapers are used to remove dried paint from the edges and surface of the blades.
The paint reservoir is comprised of a block having a slit therein for receiving a portion of the blade in one side thereof, the slit is in fluid communication with an internal reservoir containing paint. As the blade rotates through the slit, paint contained in the reservoir is received and maintained between the teeth of the blade as the portion of the blade containing paint is rotated out of the block. As the blade continues to rotate, the teeth containing paint pass through one or more air jets directed at the teeth which remove the paint from between the teeth and transport the paint onto a print medium.
In another embodiment, a toothless wheel is provided in which paint is applied to the outer edge or rim of the wheel. The paint may be applied by a roller or other metering device. As the paint coated portion of the wheel passes through one or more air jets, the paint is blown from the edge of the wheel and onto the print medium.
While the air jets can be configured to remove nearly all of the paint from the blade, wheel or gear, for some quick drying paints or materials, there may be a need to provide a means of removing paint from the side surfaces of the blade, wheel or gear. As such, various scrapers may be positioned proximate or in contact with the surface of the blade to be cleaned so that upon rotation of the blade, the scraper can remove any paint deposited thereon. Such paint removal keeps the blade, wheel or gear, as the case may be, in a clean condition to ensure that the amount of paint being metered by the blade, wheel or gear is relatively precisely controlled.
Digital painting in each color occurs by using a computer to selectively control the advancing a paint coated blade or wheel through an air stream to remove the paint and project it onto a surface. The air stream remains relatively constant. Paint modulation for digital printing is achieved by the controlled advancement of the wheel through the air stream. By including multiple blades or wheels associated with multiple paint colors and controlling the position of each blade or wheel relative to the medium, digital painting can be accomplished to reproduce a preselected digital image onto a selected medium.
The present invention may be employed to apply paint to various medium regardless of the porosity of such medium. For example, grass fields, carpets and building drapes can be digitally painted with the printing device and techniques of the present invention.
It is also contemplated that the present invention may be employed to deposit other liquid, liquid-based or bondable materials onto or toward a surface in a relatively precise and controlled manner. That is, there is often a need to apply oils, finish materials, such as acrylics or polyurethanes to a surface in a controlled manner to produce a desired result, such as film thickness. Additionally, the present invention may be employed to apply such materials as etchants for glass applications as well as materials that may be employed in various masking operations, such as photo resists. The present invention, while being described with reference to xe2x80x9cdigital printingxe2x80x9d by way of example may employ such instruments and techniques to other applications in various other fields of art.